Signal processing apparatus and method, and program

ABSTRACT

Signals are provided which allow colors in a wider color range than predetermined standards, which can be handled by apparatus according to such predetermined standards. A primary color converter converts first color signals having primary color points in a wider color range than the primary color points according to BT.709 into second color signals based on the primary colors according to BT.709. A photoelectric transducer converts the second color signals into third color signals according to photoelectric transducer characteristics defined in a numerical range wider than a range from 0 to 1.0 of color signals corresponding to a luminance signal and color difference signals according to BT. 709. A color signal converter converts the third color signals into a luminance signal and color difference signals. A corrector incorporated in the color signal converter corrects the color difference signals into color difference signals.

TECHNICAL FIELD

The present invention relates to a signal processing apparatus, a signalprocessing method, and a program, and more particularly to a signalprocessing apparatus, a signal processing method, and a program forexpressing colors in a color range wider than a conventional color rangein the processing of an image signal.

BACKGROUND ART

In recent years, advances in the image processing technology haveachieved higher image quality in video cameras for capturing andrecording images and television receivers for displaying capturedimages, and have made it possible for present video cameras andtelevision receivers to reproduce sharper images than conventional videocameras and television receivers.

FIG. 1 of the accompanying drawings shows an AV (Audio Visual) systemincluding a video camera and a television receiver. In FIG. 1, a signalof an image captured by a video camera 1 is supplied through a recordingmedium 11 or a network 12 to a television receiver 2, which displays theimage captured by the video camera 1.

Details of the video camera 1 and the television receiver 2 will bedescribed below with reference to FIGS. 2 and 3 of the accompanyingdrawings.

FIG. 2 shows in block form details of the video camera 1 illustrated inFIG. 1. The video camera 1 performs its processing operation accordingto predetermined standards (e.g., ITU-R (International TelecommunicationUnion Radiocommunication sector) BT (Broadcasting service(Television)).601 (hereinafter referred to as BT.601) or ITU-R BT.709(hereinafter referred to as BT.709)). It is assumed here that the videocamera 1 performs its processing operation according to BT.709.

In FIG. 2, the video camera 1 includes a operation unit 21, an imagecapturing unit 22, an A/D converter 23, a primary color converter 24, acolor signal corrector 25, a photoelectric transducer 26, a color signalconverter 27, an encoder 28, a controller 29, a recorder 30, and acommunication unit 31.

The operation unit 21 is operated by the user when the user entersvarious commands into the video camera 1. The operation unit 21 suppliessignals representing the execution of processing sequences that areindicated by the operation by the user of the operation unit 21, toblocks that perform the respective processing sequences. For example,the operation unit 21 supplies the image capturing unit 22 with a signalrepresenting the capturing of an image, and also supplies the controller29 with a signal representing a destination of a signal (hereinafterreferred to as an image signal) indicative of an image captured by theimage capturing unit 22.

The image capturing unit 22 starts or stops an image capturing processaccording to an instruction from the operation unit 21. The imagecapturing unit 22 supplies an image signal indicative of an imagecaptured by the image capturing unit 22 to the A/D (Analog/Digital)converter 23. The image capturing unit 22 includes a CMOS (ComplementaryMetal Oxide Semiconductor) imager, a CCD (Charge Coupled Device), or thelike, and outputs color signals R, G, B (Red, Green, Blue) as an imagesignal.

The A/D converter 23 converts analog color signals supplied from theimage capturing unit 22 into digital color signals, and supplies thedigital color signals to the primary color converter 24. The colorsignals R, G, B that are supplied from the A/D converter 23 to theprimary color converter 24 are referred to as color signals R_(org),G_(org), B_(org).

The primary color converter 24 converts the color signals R_(org),G_(org), B_(org) supplied from the A/D converter 23 into color signalsR₇₀₉, G₇₀₉, B₇₀₉ based on primary colors under BT.709, and supplies thecolor signals R₇₀₉, G₇₀₉, B₇₀₉ to the color signal corrector 25.Specifically, the primary color converter 24 converts the color signalsR_(org), G_(org), B_(org) supplied from the A/D converter 23 into colorsignals R₇₀₉, G₇₀₉, B₇₀₉ based on primary colors under BT.709 accordingto the following equation (1):

$\begin{matrix}{\begin{pmatrix}R_{709} \\G_{709} \\B_{709}\end{pmatrix} = {\begin{pmatrix}1.5968 & {- 0.6351} & 0.0383 \\{- 0.1464} & 1.2259 & {- 0.0795} \\{- 0.0141} & {- 0.1086} & 1.1227\end{pmatrix}\begin{pmatrix}R_{org} \\G_{org} \\B_{org}\end{pmatrix}}} & (1)\end{matrix}$

The matrixes of the equation (1) differ depending on the primary colorpoints of the image capturing unit 22.

The color signal corrector 25 corrects the color signals R₇₀₉, G₇₀₉,B₇₀₉ supplied from the primary color converter 24 into color signalsR₇₀₉, G₇₀₉, B₇₀₉ in a numerical range from 0 to 1.0 defined according toBT.709. Specifically, the color signal corrector 25 corrects colorsignals R₇₀₉, G₇₀₉, B₇₀₉ which are smaller than 0 into 0, i.e., clipscolor signals R₇₀₉, G₇₀₉, B₇₀₉, and corrects color signals R₇₀₉, G₇₀₉,B₇₀₉ which are greater than 1.0 into 1.0, and supplies the correctedcolor signals R₇₀₉, G₇₀₉, B₇₀₉ to the photoelectric transducer 26. It isassumed that the numerical values 0, 1.0 of the numerical range from 0to 1.0 are minimum and maximum values, respectively, of the colorsignals R₇₀₉, G₇₀₉, B₇₀₉ according to BT.709.

The photoelectric transducer 26 converts the color signals R₇₀₉, G₇₀₉,B₇₀₉ supplied from the color signal corrector 25 into color signalsR′₇₀₉, G′₇₀₉, B′₇₀₉ that are corrected with the γ of a display mechanismof B.709 (the nonlinearity of light emission luminance with respect tothe image signal) according to photoelectric transducer characteristicsaccording to BT.709, and supplies the converted color signals R′₇₀₉,G′₇₀₉, B′₇₀₉ to the color signal converter 27.

Specifically, the photoelectric transducer 26 converts the color signalsR₇₀₉, G₇₀₉, B₇₀₉ into color signals R′₇₀₉, G′₇₀₉, B′₇₀₉ according to thefollowing equation (2) and supplies the converted color signals R′₇₀₉,G′₇₀₉, B′₇₀₉ to the color signal converter 27:R′ ₇₀₉=1.099×(R ₇₀₉)^(0.45)−0.099 0.018≦R ₇₀₉≦1.0 R′ ₇₀₉=4.5×R ₇₀₉ 0≦R₇₀₉<0.018  (2)

The photoelectric transducer characteristics between the color signalR₇₀₉ and the color signal R′₇₀₉ are defined in the range from theminimum value to the maximum value of the color signal R₇₀₉ according toBT.709, i.e., in the range from 0 to 1.0. The photoelectric transducercharacteristics between the color signal G₇₀₉ and the color signal G′₇₀₉and the photoelectric transducer characteristics between the colorsignal B₇₀₉ and the color signal B′₇₀₉ are also similarly defined.

The color signal converter 27 converts the color signals R′₇₀₉, G′₇₀₉,B′₇₀₉ supplied from the photoelectric transducer 26 into a luminancesignal Y′₇₀₉ and color difference signals Cb′₇₀₉, Cr′₇₀₉ under BT.709according to the equation (3) shown below, and supplies the luminancesignal Y′₇₀₉ and the color difference signals Cb′₇₀₉, Cr′₇₀₉, eachexpressed in 8 bits, to the encoder 28.

$\begin{matrix}{\begin{pmatrix}Y_{709}^{\prime} \\{Cb}_{709}^{\prime} \\{Cr}_{709}^{\prime}\end{pmatrix} = {\begin{pmatrix}0.2126 & 0.7152 & 0.0722 \\{- 0.1146} & {- 0.3854} & 0.5000 \\0.5000 & {- 0.4542} & {- 0.0458}\end{pmatrix}\begin{pmatrix}R_{709}^{\prime} \\G_{709}^{\prime} \\B_{709}^{\prime}\end{pmatrix}}} & (3)\end{matrix}$

The matrixes of the equation (3) are matrixes prescribed for 1125/60/2:1Signal Format under BT.709.

According to BT.709, the luminance signal Y′₇₀₉ generated by the colorsignal converter 27 according to the equation (3) is of value in anumerical range from 0 to 1.0. Each of the color difference signalsCb′₇₀₉, Cr′₇₀₉ generated by the color signal converter 27 according tothe equation (3) is of value in a numerical range from −0.5 to 0.5.

Furthermore, the color signal converter 27 assigns the luminance signalY′₇₀₉ in the numerical range from 0 to 1.0, which is generated by thecolor signal converter 27 according to the equation (3), to an integralvalue in an integral range from 16 to 235 which is smaller than anintegral range from 0 to 255 that can be expressed in 8 bits, andsupplies the luminance signal Y′₇₀₉ that is assigned to the integralvalue as a luminance signal according to BT.709 to the encoder 28. Thecolor signal converter 27 assigns each of the color difference signalsCb′₇₀₉, Cr′₇₀₉ in the numerical range from −0.5 to 0.5, which isgenerated by the color signal converter 27 according to the equation(3), to an integral value in an integral range from 16 to 240 which issmaller than the integral range from 0 to 255 that can be expressed in 8bits, and supplies the color difference signals Cb′₇₀₉, Cr′₇₀₉ that areassigned to the integral value as color difference signals according toBT.709 to the encoder 28.

The encoder 28 encodes the luminance signal Y′₇₀₉ and the colordifference signals Cb′₇₀₉, Cr′₇₀₉, each in 8 bits, supplied from thecolor signal converter 27 according to a predetermined format, forexample, such as MPEG (Moving Picture Experts Group) and supplies theresultant encoded data to the controller 29.

The controller 29 supplies the encoded data supplied from the encoder 28to the recorder 30 or the communication unit 31 according to aninstruction from the operation unit 21.

The recorder 30 records the encoded data supplied from the controller 29in the recording medium 11 shown in FIG. 1. The communication unit 31transmits the encoded data supplied from the controller 29 through thenetwork 12 shown in FIG. 1.

FIG. 3 shows in block form the television receiver 2 shown in FIG. 1.The television receiver 2 performs its processing operation according topredetermined standards (e.g., BT.601 or BT.709). It is assumed herethat the television receiver 2 performs its processing operationaccording to BT.709.

As shown in FIG. 3, the television receiver 2 includes an image signalinput unit 41, a luminance and color difference signal converter 42, aninherent γ characteristics corrector 43, a D/A converter 44, and adisplay mechanism 45.

The image signal input unit 41 receives encoded data reproduced from therecording medium 11 or transmitted from the network 12. The image signalinput unit 41 also decodes the encoded data according to a predeterminedformat such as MPEG, for example, and supplies a luminance signal Y′₇₀₉and color difference signals Cb′₇₀₉, Cr′₇₀₉, each expressed in 8 bits,according to BT.709, which are produced from the decoded data, to theluminance and color difference signal converter 42.

The luminance and color difference signal converter 42 converts theluminance signal Y′₇₀₉ and the color difference signals Cb′₇₀₉, Cr′₇₀₉supplied from the image signal input unit 41 into color signals R′₇₀₉,G′₇₀₉, B′₇₀₉ under BT.709 according to the equation (4) shown below, andsupplies the color signals R′₇₀₉, G′₇₀₉, B′₇₀₉ to the inherent γcharacteristics corrector 43.

$\begin{matrix}{\begin{pmatrix}R_{709}^{\prime} \\G_{709}^{\prime} \\B_{709}^{\prime}\end{pmatrix} = {\begin{pmatrix}1.0000 & 0.0000 & 1.5747 \\1.0000 & {- 0.1873} & {- 0.4682} \\1.0000 & 1.8556 & 0.0000\end{pmatrix}\begin{pmatrix}Y_{709}^{\prime} \\{Cb}_{709}^{\prime} \\{Cr}_{709}^{\prime}\end{pmatrix}}} & (4)\end{matrix}$

The luminance signal Y′₇₀₉ according to BT.709 which is supplied fromthe image signal input unit 41 to the luminance and color differencesignal converter 42 is of an integral value in an integral range from 16to 235 which can be expressed in 8 bits, as described above. Each of thecolor difference signals Cb′₇₀₉, Cr′₇₀₉ according to BT.709 which aresupplied from the image signal input unit 41 to the luminance and colordifference signal converter 42 is of an integral value in an integralrange from 16 to 240 which can be expressed in 8 bits, as describedabove.

The luminance and color difference signal converter 42 sets theluminance signal Y′₇₀₉ of the integral value in the integral range from16 to 235, which is supplied to the luminance and color differencesignal converter 42, to a value in a numerical range from 0 to 1.0, andalso sets each of the color difference signals Cb′₇₀₉, Cr′₇₀₉ of theintegral value in the integral range from 16 to 240 to a value in anumerical range from −0.5 to 0.5. The luminance and color differencesignal converter 42 also converts the luminance signal Y′₇₀₉ expressedin the numerical range from 0 to 1.0 and the color difference signalsCb′₇₀₉, Cr′₇₀₉ expressed in the numerical range from −0.5 to 0.5 intocolor signals R′₇₀₉, G′₇₀₉, B′₇₀₉ according to the equation (4).

If the γ characteristics of the display mechanism 45 of the televisionreceiver 2 are different from the photoelectric transducercharacteristics (γ characteristics) represented by the equation (2) ofBT.709, then the inherent γ characteristics corrector 43 converts thecolor signals R′₇₀₉, G′₇₀₉, B′₇₀₉ supplied from the luminance and colordifference signal converter 42 into color signals R′₇₀₉, G′₇₀₉, B′₇₀₉according to the inherent γ characteristics of the display mechanism 45(CRT (Cathode Ray Tube) or the like) of the television receiver 2, andsupplies the color signals R′₇₀₉, G′₇₀₉, B′₇₀₉ to the D/A converter 44.

If the γ characteristics of the display mechanism 45 of the televisionreceiver 2 are identical to the photoelectric transducer characteristicsof BT.709, then the inherent γ characteristics corrector 43 is notrequired.

The D/A converter 44 converts the digital color signals R′₇₀₉, G′₇₀₉,B′₇₀₉ supplied from the inherent γ characteristics corrector 43 intoanalog color signals R′₇₀₉, G′₇₀₉, B′₇₀₉, and supplies the analog colorsignals R′₇₀₉, G′₇₀₉, B′₇₀₉ to the display mechanism 45.

The display mechanism 45 includes a CRT or the like, and displays animage based on the color signals R′₇₀₉, G′₇₀₉, B′₇₀₉ supplied from theD/A converter 44.

The color signals, the luminance signals, and the color differencesignals according to BT.709 which are processed in the video camera 1and the television receiver 2 are prescribed in RECOMMENDATION ITU-RBT.709-4.

FIG. 4 of the accompanying drawings shows the chromaticity coordinatepositions of primary colors and reference white in the CIE (CommissionInternationale de I'Eclariage) colorimetric system.

DISCLOSURE OF INVENTION

Since the color signals are processed according to the standards ofBT.709 in the video camera 1 and the television receiver 2 as describedabove, the video camera 1 and the television receiver 2 are incapable ofexpressing colors not under the standards of BT.709.

If color signals, luminance signals, and color difference signals areuniquely defined regardless of BT.709, then colors in a wide color rangecan be expressed. However, it is difficult to process the color signals,the luminance signals, and the color difference signals that are thusuniquely defined in television receivers according to BT.709.

It is therefore an object of the present invention to provide signalswhich allow colors in a wider color range than predetermined standardssuch as BT.709, for example, and which can be handled by apparatusaccording to such predetermined standards.

According to the present invention, there is provided a first signalprocessing which includes a primary color converting unit for convertingfirst color signals having primary color points in a wider color rangethan primary color points according to a predetermined standard by whichcolor difference signals having a first numerical range are assigned toan integral value in a first integral range which is smaller than anintegral range which can be expressed by a plurality of bits, intosecond color signals based on primary colors according to thepredetermined standard, a characteristics converting unit for convertingthe second color signals into third color signals according tophotoelectric transducer characteristics defined in a numerical rangewhich is greater than a numerical range of color signals correspondingto a luminance signal and color difference signals according to thepredetermined standard, a color signal converting unit for convertingthe third color signals into a luminance signal and color differencesignals, and a correcting unit for correcting the luminance signalgenerated by the color signal converting unit into a luminance signalaccording to the predetermined standard, and correcting the colordifference signals generated by the color signal converting unit intocolor difference signals in a second numerical range containing thefirst numerical range, the color difference signals being assigned to anintegral value in the second numerical range which can be expressed bythe plurality of bits.

In the first signal processing apparatus, the photoelectric transducercharacteristics are in point symmetry with respect to an origin.

In the first signal processing apparatus, all of the primary colorconverting unit, the characteristics converting unit, and the colorsignal converting unit include a single look up table.

According to the present invention, there is provided a first signalprocessing method which includes the steps of converting first colorsignals having primary color points in a wider color range than primarycolor points according to a predetermined standard by which colordifference signals having a first numerical range are assigned to anintegral value in a first integral range which is smaller than anintegral range which can be expressed by a plurality of bits, intosecond color signals based on primary colors according to thepredetermined standard, converting the second color signals into thirdcolor signals according to photoelectric transducer characteristicsdefined in a numerical range which is greater than a numerical range ofcolor signals corresponding to a luminance signal and color differencesignals according to the predetermined standard, converting the thirdcolor signals into a luminance signal and color difference signals, andcorrecting the luminance signal generated by the step of converting thethird color signals, into a luminance signal according to thepredetermined standard, and correcting the color difference signalsgenerated by the step of converting the third color signals, into colordifference signals in a second numerical range containing the firstnumerical range, the color difference signals being assigned to anintegral value in the second numerical range which can be expressed bythe plurality of bits.

According to the present invention, there is provided a first programwhich enables a computer to perform a signal processing processincluding the steps of converting first color signals having primarycolor points in a wider color range than primary color points accordingto a predetermined standard by which color difference signals having afirst numerical range are assigned to an integral value in a firstintegral range which is smaller than an integral range which can beexpressed by a plurality of bits, into second color signals based onprimary colors according to the predetermined standard, converting thesecond color signals into third color signals according to photoelectrictransducer characteristics defined in a numerical range which is greaterthan a numerical range of color signals corresponding to a luminancesignal and color difference signals according to the predeterminedstandard, converting the third color signals into a luminance signal andcolor difference signals, and correcting the luminance signal generatedby the step of converting the third color signals, into a luminancesignal according to the predetermined standard, and correcting the colordifference signals generated by the step of converting the third colorsignals, into color difference signals in a second numerical rangecontaining the first numerical range, the color difference signals beingassigned to an integral value in the second numerical range which can beexpressed by the plurality of bits.

According to the present invention, there is provided a second signalprocessing apparatus wherein a luminance signal and color differencesignals include a luminance signal and color difference signals obtainedby converting first color signals having primary color points in a widercolor range than primary color points according to a predeterminedstandard by which color difference signals having a first numericalrange are assigned to an integral value in a first integral range whichis smaller than an integral range which can be expressed by a pluralityof bits, into second color signals based on primary colors according tothe predetermined standard, converting the second color signals intothird color signals according to photoelectric transducercharacteristics defined in a numerical range which is greater than anumerical range of color signals corresponding to a luminance signal andcolor difference signals according to the predetermined standard, andconverting the third color signals into a luminance signal and colordifference signals, wherein the luminance signal includes a luminancesignal according to the predetermined standard and the color differencesignals include color difference signals in a second numerical rangecontaining the first numerical range, the color difference signals beingassigned to an integral value in the second numerical range which can beexpressed by the plurality of bits, wherein the signal processingapparatus includes a luminance and color difference signal convertingunit for converting the luminance signal according to the predeterminedstandard and the color difference signals in the second numerical rangeinto the third color signals, a characteristic converting unit forconverting the third color signals into the second color signalsaccording to the photoelectric transducer characteristics, a primarycolor converting unit for converting the second color signals into thefirst color signals, and a correcting unit for correcting the firstcolor signals into signals in a numerical range which can be displayedby a display mechanism for displaying an image.

In the second signal processing apparatus, the photoelectric transducercharacteristics are in point symmetry with respect to an origin.

In the second signal processing apparatus, all of the luminance andcolor difference signal converting unit, the characteristics convertingunit, and the primary color converting unit include a single look uptable.

According to the present invention, there is provided a second signalprocessing method wherein the luminance signal and the color differencesignals include a luminance signal and color difference signals obtainedby converting first color signals having primary color points in a widercolor range than primary color points according to a predeterminedstandard by which color difference signals having a first numericalrange are assigned to an integral value in a first integral range whichis smaller than an integral range which can be expressed by a pluralityof bits, into second color signals based on primary colors according tothe predetermined standard, converting the second color signals intothird color signals according to photoelectric transducercharacteristics defined in a numerical range which is greater than anumerical range of color signals corresponding to a luminance signal andcolor difference signals according to the predetermined standard, andconverting the third color signals into a luminance signal and colordifference signals, wherein the luminance signal includes a luminancesignal according to the predetermined standard and the color differencesignals include color difference signals in a second numerical rangecontaining the first numerical range, the color difference signals beingassigned to an integral value in the second numerical range which can beexpressed by the plurality of bits, wherein the signal processing methodincludes the steps of converting the luminance signal according to thepredetermined standard and the color difference signals in the secondnumerical range into the third color signals, converting the third colorsignals into the second color signals according to the photoelectrictransducer characteristics, converting the second color signals into thefirst color signals, and correcting the first color signals into signalsin a numerical range which can be displayed by a display mechanism fordisplaying an image.

According to the present invention, there is provided a second programfor enabling a computer to perform a signal processing process whereinthe luminance signal and the color difference signals include aluminance signal and color difference signals obtained by convertingfirst color signals having primary color points in a wider color rangethan primary color points according to a predetermined standard by whichcolor difference signals having a first numerical range are assigned toan integral value in a first integral range which is smaller than anintegral range which can be expressed by a plurality of bits, intosecond color signals based on primary colors according to thepredetermined standard, converting the second color signals into thirdcolor signals according to photoelectric transducer characteristicsdefined in a numerical range which is greater than a numerical range ofcolor signals corresponding to a luminance signal and color differencesignals according to the predetermined standard, converting the thirdcolor signals into a luminance signal and color difference signals,wherein the luminance signal includes a luminance signal according tothe predetermined standard and the color difference signals includecolor difference signals in a second numerical range containing thefirst numerical range, the color difference signals being assigned to anintegral value in the second numerical range which can be expressed bythe plurality of bits, wherein the signal processing process includesthe steps of converting the luminance signal according to thepredetermined standard and the color difference signals in the secondnumerical range into the third color signals, converting the third colorsignals into the second color signals according to the photoelectrictransducer characteristics, converting the second color signals into thefirst color signals, correcting the first color signals into signals ina numerical range which can be displayed by a display mechanism fordisplaying an image.

With the first signal processing apparatus, the first signal processingmethod, and the first program according to the present invention, firstcolor signals having primary color points in a wider color range thanprimary color points according to a predetermined standard by whichcolor difference signals having a first numerical range are assigned toan integral value in a first integral range which is smaller than anintegral range which can be expressed by a plurality of bits, areconverted into second color signals based on primary colors according tothe predetermined standard, the second color signals are converted intothird color signals according to photoelectric transducercharacteristics defined in a numerical range which is greater than anumerical range of color signals corresponding to a luminance signal andcolor difference signals according to the predetermined standard. Thethird color signals are converted into a luminance signal and colordifference signals, and the luminance signal is corrected into aluminance signal according to the predetermined standard, and the colordifference signals are corrected into color difference signals in asecond numerical range containing the first numerical range, the colordifference signals being assigned to an integral value in the secondnumerical range which can be expressed by the plurality of bits.

With the second signal processing apparatus, the second signalprocessing method, and the second program according to the presentinvention, a luminance signal and color difference signals include aluminance signal and color difference signals obtained by convertingfirst color signals having primary color points in a wider color rangethan primary color points according to a predetermined standard by whichcolor difference signals having a first numerical range are assigned toan integral value in a first integral range which is smaller than anintegral range which can be expressed by a plurality of bits, intosecond color signals based on primary colors according to thepredetermined standard, converting the second color signals into thirdcolor signals according to photoelectric transducer characteristicsdefined in a numerical range which is greater than a numerical range ofcolor signals corresponding to a luminance signal and color differencesignals according to the predetermined standard, and converting thethird color signals into a luminance signal and color differencesignals, wherein the luminance signal includes a luminance signalaccording to the predetermined standard and the color difference signalsinclude color difference signals in a second numerical range containingthe first numerical range, the color difference signals being assignedto an integral value in the second numerical range which can beexpressed by the plurality of bits. The luminance signal according tothe predetermined standard and the color difference signals in thesecond numerical range are converted into the third color signals, andthe third color signals are converted into the second color signalsaccording to the photoelectric transducer characteristics. The secondcolor signals are converted into the first color signals, and the firstcolor signals are corrected into signals in a numerical range which canbe displayed by a display mechanism for displaying an image.

According to the present invention, colors in a wide color range can beexpressed by signals that can be handled by predetermined standards suchas BT.709, for example.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a conventional AV system.

FIG. 2 is a block diagram of a video camera of the conventional AVsystem shown in FIG. 1.

FIG. 3 is a block diagram of a television receiver of the conventionalAV system shown in FIG. 1.

FIG. 4 is a diagram showing primary colors and reference white accordingto ITU-R B.709.

FIG. 5 is a diagram showing the relationship between signal levels ofsignals according to various standards and integral values representingthe signals levels.

FIG. 6 is a diagram showing photoelectric transducer characteristicsemployed by the present invention.

FIG. 7 is a diagram showing the relationship between a color spacecovered by ITU-R B.709 and a color space based on to 768 colors of theMunsell color cascade and sRGB standards.

FIG. 8 is a diagram showing the relationship between a color space basedon a luminance signal and color difference signals according to thepresent invention, a color signal based on 768 colors of the Munsellcolor cascade and color signals under BT.709, and a color space based ona luminance signal and color difference signals according to BT.709.

FIG. 9 is a diagram showing the relationship of FIG. 8 as projected inthe direction of Cb′.

FIG. 10 is a diagram showing coverages in the color spaces covered byBT.709 and the present invention.

FIG. 11 is a block diagram of an AV system according to the presentinvention.

FIG. 12 is a block diagram of a video camera of the AV system shown inFIG. 11.

FIG. 13 is a flowchart of an image capturing and recording processperformed by the video camera shown in FIG. 12.

FIG. 14 is a block diagram of a television receiver of the AV systemshown in FIG. 11.

FIG. 15 is a flowchart of an image displaying process performed by thetelevision receiver shown in FIG. 14.

FIG. 16 is a diagram showing flows of signals in the processes performedby the video camera shown in FIG. 12 and the television receiver shownin FIG. 14.

FIG. 17 is a block diagram of a personal computer.

BEST MODE FOR CARRYING OUT THE INVENTION

Prior to the description of an embodiment of the present invention, acolor space employed by the embodiment of the present invention will bedescribed below in comparison with existing color spaces according tointernational standards.

FIG. 5 shows the relationship between signal levels of signals accordingto international standards and integral values representing thosesignals levels.

According to sRGB standards for a color space prescribed by IEC(International Electrotechnical Commission), 8 bits are used to expresscolor signals R, G, B, and the signal levels of the color signals R, G,B ranging from 0 to 1.0 are assigned to values ranging from 0 to 255which can be expressed by 8 bits. Each of the color signals R, G, B isrepresented by 256 (=255−0+1) gradations.

According to sYCC standards for a luminance signal and color differencesignals for still images, the luminance signal Y is expressed using 8bits as with the sRGB standards, and the signal level of the luminancesignal Y ranging from 0 to 1.0 is assigned to values ranging from 0 to255 which can be expressed by 8 bits. The luminance signal Y isrepresented by 256 (=255−0+1) gradations.

The color difference signals Cb, Cr are expressed using 8 bits, and thesignal levels of the color difference signals Cb, Cr ranging from −0.5to 0.5 are assigned to values ranging from 0 to 255 which can beexpressed by 8 bits. The color difference signals Cb, Cr are representedby 256 (=255−0+1) gradations.

Color signals, luminance signals, and color difference signals accordingto BT.601 standards for SDTV (Standard Definition Television) and BT.709standards for HDTV (High Definition Television) will be described below.

According to BT.709, 8 bits are used to express color signals R, G, B,and the signal levels of the color signals R, G, B ranging from 0 to 1.0are assigned to integral values in an integral range from 16 to 235which is smaller than the range from 0 to 255 that can be expressed by 8bits. Each of the color signals R, G, B is represented by 220(=235−16+1) gradations.

According to BT.709, 8 bits are used to express a luminance signal Y,and the signal level of the luminance signal Y ranging from 0 to 1.0 isassigned to integral values in an integral range from 16 to 235 which issmaller than the range from 0 to 255 that can be expressed by 8 bits.The luminance signal Y is represented by 220 (=235−16+1) gradations.

According to BT.709, 8 bits are used to express color difference signalsCb, Cr, and the signal levels of the color difference signals Cb, Crranging from −0.5 to 0.5 are assigned to integral values in an integralrange from 16 to 240 which is smaller than the range from 0 to 255 thatcan be expressed by 8 bits. Each of the color difference signals Cb, Cris represented by 225 (=240−16+1) gradations.

The color signals, the luminance signal, and the color differencesignals according to BT.601 are prescribed as with BT.709. According toBT.709 and BT.601, 0 and 255 of the values ranging from 0 to 255 thatare expressed by 8 bits representing signals are not used.

The color space according to the present invention will be describedbelow.

According to the present invention, the color space is based on anexpanded version of given standards wherein signals having respectivesignal levels are assigned to integral values in an integral range whichis smaller than an integral range that can be expressed by a pluralityof bits, e.g., BT.709 wherein color difference signals Cb, Cr rangingfrom −0.5 to 0.5 are assigned to integral values in an integral rangefrom 16 to 240 which is smaller than the range from 0 to 255 that can beexpressed by 8 bits.

Specifically, according to the present invention, a luminance signal Yis defined as with BT.709. That is, 8 bits are used to express theluminance signal Y, and the signal level of the luminance signal Yranging from 0 to 1.0 is assigned to integral values in an integralrange from 16 to 235 which is smaller than the range from 0 to 255 thatcan be expressed by 8 bits. Therefore, the luminance signal Y having thesignal level ranging from 0 to 1.0 is represented by 220 (=235−16+1)gradations as with BT.709.

According to the present invention, 8 bits are used to express colordifference signals Cb, Cr, and the signal levels of the color differencesignals Cb, Cr ranging from −0.5 to 0.5 are assigned to integral valuesin an integral range from 16 to 240 which is smaller than the range from0 to 255 that can be expressed by 8 bits, as with BT.709.

However, an integral range to which the signal levels of the colordifference signals Cb, Cr are assigned is expanded to an integral rangefrom 1 to 254 which contains the integral range from 16 to 240 to whichsignal levels are assigned according to BT.709. Specifically, accordingto the present invention, as with BT.709, each of the color differencesignals Cb, Cr ranging from −0.5 to 0.5 is assigned to an integral rangeof 225 (=240−16+1) gradations from 16 to 240, and the signal levels forthe integral range from 16 to 240 are also assigned to an integral rangefrom 1 to 15 and an integral range from 241 to 254.

As a result, signal levels ranging from −0.57 to 0.56 are assigned to anintegral range from 1 to 254. Consequently, according to the presentinvention, the color difference signals Cb, Cr whose signal levels arein the range from −0.57 to 0.56 are represented by 254 (=254−1+1)gradations.

As described above, according to the present invention, color differencesignals Cb, Cr whose signal levels are in the range from −0.57 to 0.56,which includes color difference signals Cb, Cr of BT.709 ranging from−0.5 to 0.5 can be realized.

According to the present invention, therefore, it is possible to expresscolors in a wider color range than the colors that can be expressedaccording to BT.709.

The luminance signal Y according to the present invention is identicalto the luminance signal Y according to BT.709, and the color differencesignals Cb, Cr according to the present invention are identical to thecolor difference signals Cb, Cr according to BT.709 with respect to thesignal levels ranging from −0.5 to 0.5 that are assigned to the integralrange from 16 to 240. Therefore, the luminance signal Y and the colordifference signals Cb, Cr according to the present invention can behandled by apparatus according to BT.709, and can be used to displayimages in a range of colors that can be expressed by BT.709, forexample.

According to the present invention, since the color difference signalsCb, Cr can have signal levels in the range from −0.57 to 0.56 which iswider than the range from −0.5 to 0.5, when the luminance signal Y andthe color difference signals Cb, Cr according to the present inventionare converted into color signals R, G, B, the signal levels of the colorsignals R, G, B can be of values out of the range from 0 to 1.0, i.e.,can be of values less than 0 (negative values) or values greater than 1.The value 0 represents the minimum value of the color signals R, G, Baccording to BT.709, and the value 1 represents the maximum value of thecolor signals R, G, B according to BT.709.

As described above, according to the present invention, color signals R,G, B having negative values or values in excess of 1 can be handled, andmutual conversion is performed between such color signals R, G, B andthe luminance signal Y ranging form 0 to 1.0 and the color differencesignals Cb, Cr ranging from −0.57 to 0.56.

When an image is captured and color signals R, G, B of the image are tobe converted into the luminance signal Y and the color differencesignals Cb, Cr according to the present invention, if the luminancesignal Y and the color difference signals Cb, Cr according to thepresent invention are to be handled by apparatus according to BT.709, itis necessary to convert the color signals R, G, B, which are to beconverted into the luminance signal Y and the color difference signalsCb, Cr according to the present invention, into color signals R, G, Baccording to the photoelectric transducer characteristics of the displaymechanism of BT.709 (γ correction)

According to BT.709, photoelectric transducer characteristics aredefined with respect to the range from 0 to 1.0 that the color signalsR, G, B can have, but no photoelectric transducer characteristics aredefined with respect to negative values and values in excess of 1.0.

Since the color signals R, G, B to be converted into the luminancesignal Y and the color difference signals Cb, Cr according to thepresent invention can have negative values and values in excess of 1.0,it is necessary to determine photoelectric transducer characteristicsaccording to which the color signals R, G, B that can have negativevalues and values in excess of 1.0 are to be converted.

According to the present invention, the photoelectric transducercharacteristics prescribed under BT.709 are applied to input values inthe range in excess of 1.0. For input values in the range of negativevalues, the photoelectric transducer characteristics prescribed underBT.709 are expanded in point symmetry with respect to the origin, andthe expanded photoelectric transducer characteristics are applied tothose negative input values.

FIG. 6 shows photoelectric transducer characteristics that are employedaccording to the present invention.

The photoelectric transducer characteristics according to the presentinvention as shown in FIG. 6 are identical to the photoelectrictransducer characteristics according to BT.709 insofar as the inputsignals (color signals R, G, B) are in the range from 0 to 1.0.

Specifically, the portion of the photoelectric transducercharacteristics shown in FIG. 6 wherein the input signals are in therange from 0 to 1.0 is expressed according to the equation (2) asdefined under BT.709.

The portion of the photoelectric transducer characteristics shown inFIG. 6 wherein the input signals are in the range exceeding 1.0 is anexpansion of the range from 0.018 to 1.0 according to the equation (2).The portion of the photoelectric transducer characteristics shown inFIG. 6 wherein the input signals are in the range of negative values isan expansion of the photoelectric transducer characteristics accordingto BT.709 in point symmetry with respect to the origin.

Therefore, the photoelectric transducer characteristics according to thepresent invention are expressed by the following equation (5):R′ _(ex709)=1.099×(R _(ex709))^(0.45)−0.099 0.018≦R _(ex709) R′_(ex709)=4.5×R _(ex709)−0.018≦R _(ex709)<0.018 R′ _(ex709)=−(1.099×(−R_(ex709))^(0.45)−0.099) R _(ex709)<−0.018  (5)

In the equation (5), R represents a color signal R before it isconverted according to the photoelectric transducer characteristics, andR′ represents a color signal R after it is converted according to thephotoelectric transducer characteristics. According to the presentinvention, color signals G, B are also converted according to theequation (5).

Colors that can be expressed according to the present invention will bedescribed below.

FIG. 7 shows the relationship between a color space covered by BT.709and a color space based on to 768 colors of high-color-saturation chromacalled the Munsell color cascade and sRGB standards.

Color signals R, G, B are converted according to the photoelectrictransducer characteristics, and the converted color signals R, G, Bconverted into a luminance signal Y and color difference signals Cb, Cr.In FIG. 7 (and also in FIGS. 8 and 9), a color space is expressed bythree axes which represent the luminance signal Y and the colordifference signals Cb, Cr thus generated. In FIG. 7, the luminancesignal Y and the color difference signals Cb, Cr are indicatedrespectively as a luminance signal Y′ and color difference signals Cb′,Cr′ in order to show that the luminance signal Y and the colordifference signals Cb, Cr correspond to the color signals R, G, Bconverted according to the photoelectric transducer characteristics.

In FIG. 7, the marks • represent the 768 colors of the Munsell colorcascade, and the range of a parallelepiped in a grid pattern representscolors expressed by color signals according to BT.709. The range of arectangular parallelepiped in FIG. 7 represents a range covered byluminance and color difference signals according to BT.709.

The luminance and color difference signals according to BT.709 cover thecolor space according to the sRGB standards, but cannot fully cover the768 colors of the Munsell color cascade.

FIG. 8 shows the relationship between a color space based on a luminancesignal and color difference signals according to the present invention,a color signal based on 768 colors of the Munsell color cascade andcolor signals under BT.709, and a color space based on a luminancesignal and color difference signals according to BT.709.

In FIG. 8, the marks • represent the 768 colors of the Munsell colorcascade, and the range of a parallelepiped in a grid pattern representscolors expressed by color signals according to BT.709. An inner one oftwo rectangular parallelepipeds in FIG. 8 represents a range covered byluminance and color difference signals according to BT.709, and an outerrectangular parallelepipeds represents a range covered by luminance andcolor difference signals according to the present invention.

FIG. 9 shows the relationship of FIG. 8 as projected in the direction ofCb′.

In FIG. 9, the marks • represent the 768 colors of the Munsell colorcascade, and the range of a parallelepiped in a grid pattern representscolors expressed by color signals according to BT.709. An inner one oftwo rectangles in FIG. 9 represents a range covered by luminance andcolor difference signals according to BT.709, and an outer rectanglerepresents a range covered by luminance and color difference signalsaccording to the present invention.

As shown in FIGS. 8 and 9, the present invention fully covers the colorspace of 768 colors of the Munsell color cascade and color signals underBT.709.

FIG. 10 shows coverages in the color spaces covered by BT.709 and thepresent invention.

The coverage of the surface area of the 768 colors of the Munsell colorcascade is 55% in the color space of color signals under BT.709, and100% in the color space of luminance and color difference signalsaccording to the present invention.

The coverage of the volume of a uniform color space (L*a*b*) is 61% inthe color space of color signals under BT.709, and 100% in the colorspace of luminance and color difference signals according to the presentinvention.

According to the present invention, therefore, a wider color space canbe covered and colors in a wider color range can be expressed.

FIG. 11 shows in block form an AV system according to the presentinvention.

As shown in FIG. 11, the AV system includes a video camera 60 and atelevision receiver 70. In FIG. 11, a signal of an image captured by avideo camera 60 is supplied through a recording medium 11 or a network12 to the television receiver 70, which displays the image captured bythe video camera 60.

FIG. 12 shows in block form details of the video camera 60 illustratedin FIG. 11. Those parts of the video camera 60 shown in FIG. 12 whichare identical to those of the video camera 1 shown in FIG. 1 are denotedby identical reference numerals, and will not be described in detailbelow.

In FIG. 12, the video camera 60 includes a operation unit 21, an imagecapturing unit 61, an A/D converter 23, a primary color converter 62, aphotoelectric transducer 63, a color signal converter 64, a corrector64A, an encoder 28, a controller 29, a recorder 30, and a communicationunit 31.

The image capturing unit 61 starts or stops an image capturing processaccording to an instruction from the operation unit 21. The imagecapturing unit 61 supplies an image signal indicative of a capturedimage to the A/D converter 23. The image capturing unit 61 includes aCMOS (Complementary Metal Oxide Semiconductor) imager, a CCD (ChargeCoupled Device), or the like, and outputs color signals R, G, B (Red,Green, Blue) as an image signal.

The primary color points of the CMOS imager or the CCD as the imagecapturing unit 61 should be positioned in a wider color range than theprimary color points according to BT.709 in order to transmitinformation of colors in a wider color range.

The A/D converter 23 converts analog color signals R, G, B supplied fromthe image capturing unit 61 into digital color signals R, G, b, andsupplies the digital color signals R, G, B to the primary colorconverter 62. The color signals R, G, B that are supplied from the A/Dconverter 23 to the primary color converter 62 are referred to as colorsignals R_(ex), G_(ex), B_(ex).

The primary color converter 62 converts the color signals R_(ex),G_(ex), B_(ex) supplied from the A/D converter 23 into color signalsR_(ex709), G_(ex709), B_(ex709) based on primary colors under BT.709,and supplies the color signals R_(ex709), G_(ex709), B_(ex709) to thephotoelectric transducer 63. Specifically, the primary color converter62 converts the color signals R_(ex), G_(ex), B_(ex) supplied from theA/D converter 23 into color signals R_(ex709), G_(ex709), B_(ex709)based on primary colors under BT.709 according to the equation (6) shownbelow. The primary colors under BT.709 are shown in FIG. 4.

$\begin{matrix}{\begin{pmatrix}R_{{ex}\; 709} \\G_{{ex}\; 709} \\B_{{ex}\; 709}\end{pmatrix} = {\begin{pmatrix}1.5968 & {- 0.6351} & 0.0383 \\{- 0.1464} & 1.2259 & {- 0.0795} \\{- 0.0141} & {- 0.1086} & 1.1227\end{pmatrix}\begin{pmatrix}R_{ex} \\G_{ex} \\B_{ex}\end{pmatrix}}} & (6)\end{matrix}$

The color signals R_(ex709), G_(ex709), B_(ex709) obtained by theprimary color conversion performed by the primary color converter 62 canbe of negative values or values in excess of 1 if the primary colorpoints of the image capturing unit 61 are different from the primarycolor points of BT.709.

The photoelectric transducer 63 converts the color signals R_(ex709),G_(ex709), B_(ex709) supplied from the primary color converter 62 intocolor signals R′_(ex709), G′_(ex709), B′_(ex709) according to thephotoelectric transducer characteristics of present invention, andsupplies the converted color signals R′_(ex709), G′_(ex709), B′_(ex709)to the color signal converter 64.

That is, the photoelectric transducer 63 converts the color signalsR_(ex709), G_(ex709), B_(ex709) supplied from the primary colorconverter 62 into color signals R′_(ex709), G′_(ex709), B′_(ex709)according to the equation (5), and supplies the converted color signalsR′_(ex709), G′_(ex709), B′_(ex709) to the color signal converter 64.

The equation (5) is an equation for converting the color signalR_(ex709) into the color signal R′_(ex709). The color signals G_(ex709),B_(ex709) are also converted respectively into the color signalsG′_(ex709), B′_(ex709) according to the equation (5) as with the colorsignal R_(ex709).

The range from 0 to 1.0 of the color signals R′_(ex709), G′_(ex709),B′_(ex709) which are converted from the color signals R_(ex709),G_(ex709), B_(ex709) by the photoelectric transducer 63 based on thephotoelectric transducer characteristics according to the presentinvention is the same as with BT.709.

The color signal converter 64 converts the color signals R′_(ex709),G′_(ex709), B′_(ex709) supplied from the photoelectric transducer 63into a luminance signal Y′_(ex709) and color difference signalsCb′_(ex709), Cr′_(ex709) according to the equation (7) shown below. Thecolor signal converter 64 has the corrector 64A incorporated therein.The corrector 64A corrects the luminance signal Y′_(ex709) into aluminance signal in a numerical range from 0 to 1.0 defined according tothe present invention, and corrects the color difference signalsCb′_(ex709), Cr′_(ex709) into color difference signals in a numericalrange from −0.57 to 0.56 defined according to the present invention, andsupplies the corrected luminance signal and the corrected colordifference signals to the encoder 28.

$\begin{matrix}{\begin{pmatrix}Y_{{ex}\; 709}^{\prime} \\{Cb}_{{ex}\; 709}^{\prime} \\{Cr}_{{ex}\; 709}^{\prime}\end{pmatrix} = {\begin{pmatrix}0.2126 & 0.7152 & 0.0722 \\{- 0.1146} & {- 0.3854} & 0.5000 \\0.5000 & {- 0.4542} & {- 0.0458}\end{pmatrix}\begin{pmatrix}R_{{ex}\; 709}^{\prime} \\G_{{ex}\; 709}^{\prime} \\B_{{ex}\; 709}^{\prime}\end{pmatrix}}} & (7)\end{matrix}$

Specifically, the corrector 64A of the color signal converter 64corrects the luminance signal Y′_(ex709) which is smaller than 0 into 0and corrects the luminance signal Y′_(ex709) which is greater than 1.0into 1.0, for example. The corrector 64A also corrects the colordifference signals Cb′_(ex709), Cr′_(ex709) which are smaller than −0.57into −0.57, and corrects the color difference signals Cb′_(ex709),Cr′_(ex709) which are greater than 0.56 into 0.56. The corrector 64Aassigns the corrected luminance signal Y′_(ex709) to an integral valuein an integral range from 16 to 235 which is smaller than the integralrange from 0 to 255 that can be expressed in 8 bits, and supplies theluminance signal Y′_(ex709) that is assigned to the integral value as aluminance signal according to the present invention to the encoder 28.The corrector 64A assigns the corrected color difference signalsCb′_(ex709), Cr′_(ex709) to an integral value in an integral range from1 to 254 which is smaller than the integral range from 0 to 255 that canbe expressed in 8 bits, and supplies the color difference signalsCb′_(ex709), Cr′_(ex709) that is assigned to the integral value as colordifference signals according to the present invention to the encoder 28.

An image capturing and recording process performed by the video camera60 shown in FIG. 12 will be described below with reference to FIG. 13.

The operation unit 21 instructs the image capturing unit 61 to startcapturing an image and at the same time instructs the controller 29 tostart recording a captured image, i.e., to control the recorder 30 torecord a captured image. In this manner, the image capturing andrecording process is started.

In step S1 shown in FIG. 13, the image capturing unit 61 captures animage of a subject to acquire an image signal, and supplies colorsignals R, G, B as the image signal to the A/D converter 23. Then,control goes to step S2.

In step S2, the A/D converter 23 converts the analog color signals R, G,B supplied from the image capturing unit 61 into digital color signalsR, G, B, and supplies the digital color signals R_(ex), G_(ex), B_(ex)to the primary color converter 62. Then, control goes to step S3.

In step S3, the primary color converter 62 converts the color signalsR_(ex), G_(ex), B_(ex) supplied from the A/D converter 23 into colorsignals R_(ex709), G_(ex709), B_(ex709) based on primary colors underBT.709, and supplies the color signals R_(ex709), G_(ex709), B_(ex709)to the photoelectric transducer 63. Then, control goes to step S4.

In step S4, the photoelectric transducer 63 converts the color signalsR_(ex709), G_(ex709), B_(ex709) supplied from the primary colorconverter 62 into color signals R′_(ex709), G′_(ex709), B′_(ex709) basedon the photoelectric transducer characteristics according to the presentinvention, and supplies the converted color signals R′_(ex709),G′_(ex709), B′_(ex709) to the color signal converter 64. Then, controlgoes to step S5.

In step S5, the color signal converter 64 converts the color signalsR′_(ex709), G′_(ex709), B′_(ex709) supplied from the photoelectrictransducer 63 into a luminance signal Y′_(ex709) and color differencesignals Cb′_(ex709), Cr′_(ex709) according to the present invention.Then, control goes to step S6.

In step S6, the corrector 64A of the color signal converter 64 correctsinvalid values of the luminance signal Y′_(ex709) and the colordifference signals Cb′_(ex709), Cr′_(ex709) which are produced in stepS5.

Specifically, the corrector 64A corrects the luminance signal Y′_(ex709)into a luminance signal Y′_(ex709) in a numerical range from 0 to 1.0defined according to the present invention, and corrects the colordifference signals Cb′_(ex709), Cr′_(ex709) into color differencesignals Cb′_(ex709), Cr′_(ex709) in a numerical range from −0.57 to 0.56defined according to the present invention. For example, the corrector64A corrects the luminance signal Y′_(ex709) which is smaller than 0into 0 and corrects the luminance signal Y′_(ex709) which is greaterthan 1.0 into 1.0. The corrector 64A also corrects the color differencesignals Cb′_(ex709), Cr′_(ex709) which are smaller than −0.57 into−0.57, and corrects the color difference signals Cb′_(ex709),Cr′_(ex709) which are greater than 0.56 into 0.56. The corrector 64Aexpresses the corrected luminance signal Y′_(ex709) and the correctedcolor difference signals Cb′_(ex709), Cr′_(ex709) according to thepresent invention with the 8 bits described with reference to FIG. 5,and supplies the luminance signal Y′_(ex709) and the color differencesignals Cb′_(ex709), Cr′_(ex709) to the encoder 28. Then, control goesto step S7.

In step S7, the encoder 28 encodes the luminance signal Y′_(ex709) andthe color difference signals Cb′_(ex709), Cr′_(ex709) supplied from thecolor signal converter 64 according to a predetermined format such asMPEG, for example, and supplies the resultant encoded data to thecontroller 29. Then, control goes to step S8.

In step S8, the controller 29 supplies the encoded data supplied fromthe encoder 28 to the recorder 30. The recorder 30 records the encodeddata supplied from the controller 29 in the recording medium 11 shown inFIG. 1. Control then goes to step S9.

In step S9, the operation unit 21 determines whether there is a requestto stop the image capturing and recording process or not.

If it is judged in step S9 that there is no request to stop the imagecapturing and recording process, then control goes back to step S1 torepeat the image capturing and recording process. If it is judged instep S9 that there is a request to stop the image capturing andrecording process, then the operation unit 21 instructs the imagecapturing unit 61 to stop capturing an image, and also instructs thecontroller 29 to stop recording a captured image. In this manner, theimage capturing and recording process is stopped.

FIG. 14 shows in block form the television receiver 70 of the AV systemshown in FIG. 11. Those parts of the television receiver 70 shown inFIG. 14 which are identical to those of the television receiver 2 shownin FIG. 3 are denoted by identical reference numerals, and will not bedescribed in detail below.

In FIG. 14, the television receiver 70 includes an image signal inputunit 41, a luminance and color difference signal converter 71, aninverse photoelectric transducer 72, a primary color converter 73, acolor signal corrector 74, an inherent γ characteristics corrector 75, aD/A converter 44, and a display mechanism 76.

The luminance and color difference signal converter 71 converts theluminance signal Y′_(ex709) and the color difference signalsCb′_(ex709), Cr′_(ex709) supplied from the image signal input unit 41into color signals R′_(ex709), G′_(ex709), B′_(ex709) based on thephotoelectric transducer characteristics according to the followingequation (8), and supplies the color signals R′_(ex709), G′_(ex709),B′_(ex709) to the inverse photoelectric transducer 72:

$\begin{matrix}{\begin{pmatrix}R_{{ex}\; 709}^{\prime} \\G_{{ex}\; 709}^{\prime} \\B_{{ex}\; 709}^{\prime}\end{pmatrix} = {\begin{pmatrix}1.0000 & 0.0000 & 1.5747 \\1.0000 & {- 0.1873} & {- 0.4682} \\1.0000 & 1.8556 & 0.0000\end{pmatrix}\begin{pmatrix}Y_{{ex}\; 709}^{\prime} \\{Cb}_{{ex}\; 709}^{\prime} \\{Cr}_{{ex}\; 709}^{\prime}\end{pmatrix}}} & (8)\end{matrix}$

Specifically, the luminance and color difference signal converter 71sets the luminance signal Y′_(ex709) of the integral value in theintegral range from 16 to 235 which can be expressed in 8 bits, to avalue in a numerical range from 0 to 1.0, and also sets each of thecolor difference signals Cb′_(ex709), Cr′_(ex709) of the integral valuein the integral range from 1 to 254 which can be expressed in 8 bits, toa value in a numerical range from −0.57 to 0.56. The luminance and colordifference signal converter 71 also converts the luminance signalY′_(ex709) expressed in the numerical range from 0 to 1.0 and the colordifference signals Cb′_(ex709), Cr′_(ex709) expressed in the numericalrange from −0.57 to 0.56 into color signals R′_(ex709), G′_(ex709),B′_(ex709) according to the equation (8).

The inverse photoelectric transducer 72 converts the color signalsR′_(ex709), G′_(ex709), B′_(ex709) supplied from the luminance and colordifference signal converter 71 according to the photoelectric transducercharacteristics of the present invention. Specifically, the inversephotoelectric transducer 72 converts the color signals R′_(ex709),G′_(ex709), B′_(ex709) supplied from the luminance and color differencesignal converter 71 into color signals R_(ex709), G_(ex709), B_(ex709)according to the following equation (9), and supplies the color signalsR_(ex709), G_(ex709), B_(ex709) to the primary color converter 73.R _(ex709)=((R′ _(ex709)+0.099)^(1/0.45)/1.099)0.081≦R′ _(ex709) R_(ex709) =R′ _(ex709)/4.5−0.081≦R′ _(ex709)<0.081 R _(ex709)=−((−R′_(ex709)+0.099)^(1/0.45)/1.099)R′ _(ex709)<−0.081  (9)

Specifically, the inverse photoelectric transducer 72 performs a processwhich is an inversion of the process performed by the photoelectrictransducer 63 of the video camera 60 (see FIG. 12) on the color signalsR′_(ex709), G′_(ex709), B′_(ex709) supplied from the luminance and colordifference signal converter 71, thereby converting the color signalsR′_(ex709), G′_(ex709), B′_(ex709) supplied from the luminance and colordifference signal converter 71 back into the color signals R_(ex709),G_(ex709), B_(ex709) prior to being converted by the photoelectrictransducer 63 of the video camera 60.

The equation (9) is an equation for converting the color signalR′_(ex709) into the color signal R_(ex709). The color signalsG′_(ex709), B′_(ex709) are also converted respectively into the colorsignals G_(ex709), B_(ex709) according to the equation (9) as with thecolor signal R′_(ex709).

The color converter 73 converts the color signals R_(ex709), G_(ex709),B_(ex709) supplied from the inverse photoelectric transducer 72 intocolor signals R_(tv), B_(tv), G_(tv) based on the primary colors of thedisplay mechanism 76, and supplies the color signals R_(tv), B_(tv),G_(tv) to the color signal corrector 74. Specifically, the primary colorconverter 73 converts the color signals R_(ex709), G_(ex709), B_(ex709)supplied from the inverse photoelectric transducer 72 into color signalsR_(tv), B_(tv), G_(tv) based on the primary colors of the displaymechanism 76 according to the following equation (10):

$\begin{matrix}{\begin{pmatrix}R_{tv} \\G_{tv} \\B_{tv}\end{pmatrix} = {\begin{pmatrix}0.6575 & 0.3408 & 0.0017 \\0.0795 & 0.8621 & 0.0583 \\0.0159 & 0.0877 & 0.8964\end{pmatrix}\begin{pmatrix}R_{{ex}\; 709} \\G_{{ex}\; 709} \\B_{{ex}\; 709}\end{pmatrix}}} & (10)\end{matrix}$

The color signal corrector 74 corrects those of the color signalsR_(tv), B_(tv), G_(tv), supplied from the primary color converter 73which cannot be displayed by the display mechanism 76, and supplies thecorrected color signals to the inherent γ characteristics corrector 75.Specifically, if the signal levels of the color signals R_(tv), B_(tv),G_(tv) supplied from the primary color converter 73 are not contained inthe range of signals levels of color signals which cannot be displayedby the display mechanism 76, then the color signal corrector 74 correctsthe color signals R_(tv), B_(tv), G_(tv) into color signals havingsignal levels which can be displayed by the display mechanism 76.

For example, if the color signals R_(tv), B_(tv), G_(tv) supplied to thecolor signal corrector 74 are of negative values, then the color signalcorrector 74 corrects the color signals R_(tv), B_(tv), G_(tv) into avalue of 0.

If the signal levels of the color signals R_(tv), B_(tv), G_(tv)supplied from the primary color converter 73 are color signals whichcannot be displayed by the display mechanism 76, then the color signalcorrector 74 may correct the color signals R_(tv), B_(tv), G_(tv) intocolor signals, which have minimum color differences with the colorsignals R_(tv), B_(tv), G_(tv), within a color range which can bedisplayed by the display mechanism 76. Alternatively, the color signalcorrector 74 may correct the color signals R_(tv), B_(tv), G_(tv) intocolor signals that keeps luminance, but has lower saturation.

The inherent γ characteristics corrector 75 converts the color signalsR_(tv), G_(tv), B_(tv) supplied from the color signal corrector 74 intocolor signals R′_(tv), G′_(tv), B′_(tv) for the display mechanism 76 inorder to inherent correct γ characteristics in the display mechanism 76of the television receiver 70, and supplies the color signals R′_(tv),G′_(tv), B′_(tv) to the D/A converter 44.

The D/A converter 44 converts the digital color signals R′_(tv),G′_(tv), B′_(tv) supplied from the inherent γ characteristics corrector75 into analog color signals R′_(tv), G′_(tv), B′_(tv), and supplies theanalog color signals R′_(tv), G′_(tv), B′_(tv) to the display mechanism76.

The display mechanism 76 includes a CRT or the like, and displays animage based on the color signals R′_(tv), G′_(tv), B′_(tv) supplied fromthe D/A converter 44. The display mechanism 76 according to the presentinvention is arranged to express, i.e., display, colors in a wider colorrange than the display mechanism 45 shown in FIG. 3.

An image display process performed by the television receiver 70 shownin FIG. 14 will be described below with reference to FIG. 15.

In step S21 shown in FIG. 15, the image signal input unit 41 acquires animage signal. The image signal input unit 41 also decodes the suppliedencoded data according to MPEG, for example, and supplies a luminancesignal Y′_(ex709) and color difference signals Cb′_(ex709), Cr′_(ex709)which are produced from the decoded data, to the luminance and colordifference signal converter 71. Then, control goes to step S22.

In step S22, the luminance and color difference signal converter 71converts the luminance signal Y′_(ex709) and the color differencesignals Cb′_(ex709), Cr′_(ex709) supplied from the image signal inputunit 41 into color signals R′_(ex709), G′_(ex709), B′_(ex709) accordingto the equation (8), and supplies the color signals R′_(ex709),G′_(ex709), B′_(ex709) to the inverse photoelectric transducer 72. Then,control goes to step S23.

In step S23, the inverse photoelectric transducer 72 converts the colorsignals R′_(ex709), G′_(ex709), B′_(ex709) supplied from the luminanceand color difference signal converter 71 into color signals R_(ex709),G_(ex709), B_(ex709) according to the equation (9), and supplies thecolor signals R_(ex709), G_(ex709), B_(ex709) to the primary colorconverter 73. Then, control goes to step S24.

In step S24, the primary color converter 73 converts the color signalsR_(ex709), G_(ex709), B_(ex709) supplied from the inverse photoelectrictransducer 72 into color signals R_(tv), G_(tv), B_(tv) based on theprimary colors of the display mechanism 76, and supplies the colorsignals R_(tv), G_(tv), B_(tv) to the color signal corrector 74. Then,control goes to step S25.

In step S25, the color signal corrector 74 corrects those of the colorsignals R_(tv), G_(tv), B_(tv), supplied from the primary colorconverter 73 which cannot be displayed by the display mechanism 76, intodisplayable color signals, and supplies the displayable color signals tothe inherent γ corrector 75. Then, control goes to step S26.

In step S26, the inherent γ corrector 75 converts the color signalsR_(tv), G_(tv), B_(tv), supplied from the color signal corrector 74 intocolor signals R′_(tv), G′_(tv), B′_(tv) according to the γcharacteristics inherent in the television receiver 70, and supplies thecolor signals R′_(tv), G′_(tv), B′_(tv) to the D/A converter 44. Then,control goes to step S27.

In step S27, the D/A converter 44 converts the digital color signalsR′_(tv), G′_(tv), B′_(tv), supplied from the inherent γ corrector 75into analog color signals R′_(tv), G′_(tv), B′_(tv), and supplies theanalog color signals R′_(tv), G′_(tv), B′_(tv) to the display mechanism76. Then, control goes to step S28.

In step S28, the display mechanism 76 displays an image based on thecolor signals R′_(tv), G′_(tv), B′_(tv), supplied from the D/A converter44. Thereafter, control goes back to step S21 to repeat the imagedisplaying process.

Flows of signals until an image captured by the video camera 1 isdisplayed by the display mechanism 70 will briefly be described belowwith reference to FIG. 16. The arrows in FIG. 16 represent processessuch as conversion processes on the signals.

Processes 81 through 83 are performed by the video camera 1, andprocesses 91 through 94 are performed by the television receiver 70.

An image captured by the image capturing unit 61 of the video camera 60is converted by the A/D converter 23 and supplied as color signalsR_(ex), G_(ex), B_(ex) based on the primary colors of the imagecapturing unit 61 (see FIG. 12) to the primary color converter 62, whichconverts the color signals R_(ex), G_(ex), B_(ex) into color signalsR_(ex709), G_(ex709), B_(ex709) based on the primary colors under BT.709(the process 81).

Thereafter, the color signals R_(ex709), G_(ex709), B_(ex709) areconverted by the photoelectric transducer 63 into color signalsR′_(ex709), G′_(ex709), B′_(ex709) according to the photoelectrictransducer characteristics of the present invention (the process 82).The color signals R′_(ex709), G′_(ex709), B′_(ex709) are converted bythe color signal converter 64 into a luminance signal Y′_(ex709) andcolor difference signals Cb′_(ex709), Cr′_(ex)709 according to thepresent invention (the process 83). The luminance signal Y′_(ex709) andthe color difference signals Cb′_(ex709), Cr′_(ex709) are encoded by theencoder 28 into encoded data, which are recorded by the recorder 30 ortransmitted through the network 12.

In the television receiver 70, the encoded data supplied from the videocamera 60 are decoded into a luminance signal Y′_(ex709) and colordifference signals Cb′_(ex709), Cr′_(ex709) according to the presentinvention. The luminance signal Y′_(ex709) and the color differencesignals Cb′_(ex709), Cr′_(ex709) are converted by the luminance andcolor difference signal converter 71 into color signals R′_(ex709),G′_(ex709), B′_(ex709) based on the photoelectric transducercharacteristics according to the present invention (the process 91).Specifically, the luminance signal Y′_(ex709) and the color differencesignals Cb′_(ex709), Cr′_(ex709) are converted back into the colorsignals R′_(ex709), G′_(ex709), B′_(ex709) generated by thephotoelectric transducer 63 of the video camera 63.

Thereafter, the color signals R′_(ex709), G′_(ex709), B′_(ex709) areconverted by the inverse photoelectric transducer 72 into color signalsR_(ex709), G_(ex709), B_(ex709) based on the primary colors of BT.709,which are generated by the primary color converter 63 of the videocamera 60 (the process 92).

The color signals R_(ex709), G_(ex709), B_(ex709) are then converted bythe primary color converter 73 into color signals R_(tv), G_(tv), B_(tv)based on the primary colors of the display mechanism 76 (see FIG. 14)(the process 93).

The color signals R_(tv), G_(tv), B_(tv) are converted by the inherent γcorrector 75 into color signals R′_(tv), G′_(tv), B′_(tv) according tothe γ characteristics inherent in the television receiver 70 (theprocess 94). An image is displayed based on the color signals R′_(tv),G′_(tv), B′_(tv) by the display mechanism 76.

As described above, the video camera 60 and the television receiver 70can reproduce colors in a wide color range that cannot be expressedaccording to BT.709 based on effective numerical values (signal ranges)of the color difference signals Cb, Cr which are expanded from thosevalues according to BT.709.

The luminance signal Y of the image captured by the video camera 60 isin compliance with BT.709, and the color difference signals Cb, Cr arealso in compliance with BT.709 with respect to the range from −0.5 to0.5. Therefore, when the luminance signal Y and color difference signalsCb, Cr are processed by a television receiver according to BT.709, thenan image can be displayed by the television receiver in the color rangeaccording to BT.709.

In the video camera 60, each of the primary color converter 62 and thecolor signal converter 64 can be implemented by a circuit forcalculating a 3×3 matrix, and the photoelectric transducer 63 can beimplemented by a one-dimensional LUT (Look Up Table). All of the primarycolor converter 62, the photoelectric transducer 63, and the colorsignal converter 64 can also be implemented by a three-dimensional LUT.

In the television receiver 70, each of the luminance and colordifference signal converter 71 and the primary color converter 73 can beimplemented by a circuit for calculating a 3×3 matrix, and each of theinverse photoelectric transducer 72 and the inherent γ corrector 75 canbe implemented by a one-dimensional LUT. All of the luminance and colordifference signal converter 71, the inverse photoelectric transducer 72,the primary color converter 73, and the inherent γ corrector 75 can alsobe implemented by a three-dimensional LUT.

In the present embodiment, the range of negative values of thephotoelectric transducer characteristics according to the presentinvention is provided as an expansion of the photoelectric transducercharacteristics according to BT.709 in point symmetry with respect tothe origin. However, the range of negative values of the photoelectrictransducer characteristics according to the present invention may not beprovided as an expansion of the photoelectric transducer characteristicsaccording to BT.709 in point symmetry with respect to the origin.Rather, the range of negative values of the photoelectric transducercharacteristics according to the present invention may be an expansionin a negative range of the photoelectric transducer characteristicsaccording to ITU-R BT.1361, for example.

In the present embodiment, the present invention is applied to anexpansion of BT.709. However, the present invention is also applicableto an expansion of other standards, e.g., BT.601. According to anexpansion of BT.601, however, matrixes used in the signal convertingprocesses are different from the matrixes according to the embodiment ofthe present invention. For example, the signal converting process thatis performed by the color signal converter 64 shown in FIG. 12 employsthe following equation (11) instead of the equation (7):

$\begin{matrix}{\begin{pmatrix}Y_{{ex}\; 601}^{\prime} \\{Cb}_{{ex}\; 601}^{\prime} \\{Cr}_{{ex}\; 601}^{\prime}\end{pmatrix} = {\begin{pmatrix}0.2990 & 0.5870 & 0.1140 \\{- 0.1687} & {- 0.3313} & 0.5000 \\0.5000 & {- 0.4187} & {- 0.0813}\end{pmatrix}\begin{pmatrix}R_{{ex}\; 601}^{\prime} \\G_{{ex}\; 601}^{\prime} \\B_{{ex}\; 601}^{\prime}\end{pmatrix}}} & (11)\end{matrix}$

Similar expansions may be applicable to other standards wherein a colordifference signal in a certain numerical range is assigned to anintegral value in an integral range which is smaller than an integralrange that can be expressed by a plurality of bits.

The above processing sequence may be performed by either hardware orsoftware.

If the processing sequence is performed by software, then a softwareprogram is downloaded from a recording medium into a computer ofdedicated hardware or a general-purpose personal computer 100 shown inFIG. 17 which is capable of performing various functions based onprograms installed therein.

As shown in FIG. 17, the recording medium includes a package medium suchas a magnetic disk 111 (including a flexible disk), an optical disk 112(including a CD-ROM (Compact bisc-Read Only Memory), a DVD (DigitalVersatile Disc), a magneto-optical disk 113 (including an MD (Mini-Disc)(trademark)), or a semiconductor memory 114, which is distributed toprovide the user with the program separately from the personal computer100, or a ROM 102 storing the program, or a hard disk incorporated inthe recorder 109, which is provided to the user as being incorporated inthe personal computer 100.

The personal computer 100 has a CPU 101 for controlling overalloperation of the personal computer 100. When the CPU 101 is suppliedwith an instruction from the user through an input unit 106 having akeyboard and a mouse via a bus 104 and input/output interface 105, theCPU 101 executes a program stored in a ROM (Read Only Memory) 102.Alternatively, the CPU 101 loads a program which is read from themagnetic disk 111, the optical disk 112, the magneto-optical disk 113 orthe semiconductor memory 114 which is connected to a drive 110 andinstalled in the recorder 109, into a RAM (Random Access Memory) 103,and executes the loaded program. The CPU 101 outputs data obtained bythe execution of the program to an output unit 107 having a display anda speaker. The CPU 101 acquires data form the input unit 106 which alsohas a tuner, a camera, or a microphone. The CPU 101 also controls acommunication unit 108 to communicate with an external circuit andexchanges data with the external circuit.

The communication unit 108 may perform wireless or wired communicationsor both wireless and wired communications. The communication unit 108 isnot limited any communication processes. For example, the communicationunit 108 may operate based on a wireless LAN (Local Area Network)according to any of various processes such as the IEEE (The Institute ofElectrical and Electronic Engineers, Inc.) 802.11a or 802.1b orBluetooth for wireless communications. The communication unit 108 mayalso operate according to any of various processes such as Ethernet(registered trademark), USB, or IEEE1394 for wired communications.

The program for performing the above processing sequence may beinstalled into the computer through a wired or wireless communicationmedium such as a local area network, the Internet, a digital satellitebroadcasting medium via an interface such as a router, a modem, or thelike, if necessary.

In the present specification, the steps that are descriptive of theprogram stored in the recording medium include not only processingdetails that are carried out chronologically in the order of the steps,but also processing details that are carried out parallel orindividually, rather than chronologically.

1. A signal processing apparatus for processing color signals andoutputting a luminance signal and color difference signals, comprising:a primary color converting unit for converting first color signalshaving primary color points in a wider color range than primary colorpoints according to a predetermined standard by which color differencesignals having a first numerical range are assigned to an integral valuein a first integral range which is smaller than an integral range whichcan be expressed by a plurality of bits, into second color signals basedon primary colors according to said predetermined standard; acharacteristics converting unit for converting said second color signalsinto third color signals according to photoelectric transducercharacteristics defined in a numerical range which is greater than anumerical range of color signals corresponding to a luminance signal andcolor, difference signals according to said predetermined standard; acolor signal converting unit for converting said third color signalsinto a luminance signal and color difference signals; and a correctingunit for correcting the luminance signal generated by said color signalconverting unit into a luminance signal according to said predeterminedstandard, and correcting the color difference signals generated by saidcolor signal converting unit into color difference signals in a secondnumerical range containing said first numerical range, said colordifference signals being assigned to an integral value in the secondnumerical range which can be expressed by said plurality of bits.
 2. Thesignal processing apparatus according to claim 1, wherein saidphotoelectric transducer characteristics are in point symmetry withrespect to an origin.
 3. The signal processing apparatus according toclaim 1, wherein all of said primary color converting unit, saidcharacteristics converting unit, and said color signal converting unitcomprise a single look up table.
 4. A signal processing method performedby a signal processing apparatus for processing color signals andoutputting a luminance signal and color difference signals, wherein thesignal processing apparatus includes a processor, the method comprisingthe steps of: converting, by the processor, first color signals havingprimary color points in a wider color range than primary color pointsaccording to a predetermined standard by which color difference signalshaving a first numerical range are assigned to an integral value in afirst integral range which is smaller than an integral range which canbe expressed by a plurality of bits, into second color signals based onprimary colors according to said predetermined standard; converting, bythe processor, said second color signals into third color signalsaccording to photoelectric transducer characteristics defined in anumerical range which is greater than a numerical range of color signalscorresponding to a luminance signal and color difference signalsaccording to said predetermined standard; converting, by the processor,said third color signals into a luminance signal and color differencesignals; and correcting, by the processor, the luminance signalgenerated by said step of converting said third color signals, into aluminance signal according to said predetermined standard, andcorrecting, by the processor, the color difference signals generated bysaid step of converting said third color signals, into color differencesignals in a second numerical range containing said first numericalrange, said color difference signals being assigned to an integral valuein the second numerical range which can be expressed by said pluralityof bits.
 5. A program on a computer-readable medium and executable by acomputer for enabling the computer to perform a signal processingprocess for processing color signals and outputting a luminance signaland color difference signals, said signal processing process comprisingthe steps of: converting first color signals having primary color pointsin a wider color range than primary color points according to apredetermined standard by which color difference signals having a firstnumerical range are assigned to an integral value in a first integralrange which is smaller than an integral range which can be expressed bya plurality of bits, into second color signals based on primary colorsaccording to said predetermined standard; converting said second colorsignals into third color signals according to photoelectric transducercharacteristics defined in a numerical range which is greater than anumerical range of color signals corresponding to a luminance signal andcolor difference signals according to said predetermined standard;converting said third color signals into a luminance signal and colordifference signals; and correcting the luminance signal generated bysaid step of converting said third color signals, into a luminancesignal according to said predetermined standard, and correcting thecolor difference signals generated by said step of converting said thirdcolor signals, into color difference signals in a second numerical rangecontaining said first numerical range, said color difference signalsbeing assigned to an integral value in the second numerical range whichcan be expressed by said plurality of bits.
 6. A signal processingapparatus for processing a luminance signal and color difference signalsand outputting color signals, wherein said luminance signal and saidcolor difference signals comprise a luminance signal and colordifference signals which have been obtained by: converting first colorsignals having primary color points in a wider color range than primarycolor points according to a predetermined standard by which colordifference signals having a first numerical range are assigned to anintegral value in a first integral range which is smaller than anintegral range which can be expressed by a plurality of bits, intosecond color signals based on primary colors according to saidpredetermined standard; converting said second color signals into thirdcolor signals according to photoelectric transducer characteristicsdefined in a numerical range which is greater than a numerical range ofcolor signals corresponding to a luminance signal and color differencesignals according to said predetermined standard; and converting saidthird color signals into-a luminance signal and color differencesignals; wherein said luminance signal comprises a luminance signalaccording to said predetermined standard and said color differencesignals comprise color difference signals in a second numerical rangecontaining said first numerical range, said color difference signalsbeing assigned to an integral value in the second numerical range whichcan be expressed by said plurality of bits, wherein said signalprocessing apparatus comprises: a luminance and color difference signalconverting unit for converting said luminance signal according to saidpredetermined standard and said color difference signals in said secondnumerical range into said third color signals; a characteristicconverting unit for converting said third color signals into said secondcolor signals according to said photoelectric transducercharacteristics; a primary color converting unit for converting saidsecond color signals into said first color signals; and a correctingunit for correcting said first color signals into signals in a numericalrange which can be displayed by a display mechanism for displaying animage.
 7. The signal processing apparatus according to claim 6, whereinsaid photoelectric transducer characteristics are in point symmetry withrespect to an origin.
 8. The signal processing apparatus according toclaim 6, wherein all of said luminance and color difference signalconverting unit, said characteristics converting unit, and said primarycolor converting unit comprise a single look up table.
 9. A signalprocessing method performed by a signal processing apparatus forprocessing a luminance signal and color difference signals andoutputting color signals, wherein the signal processing apparatusincludes a processor, wherein said luminance signal and said colordifference signals comprise a luminance signal and color differencesignals obtained by: converting first color signals having primary colorpoints in a wider color range than primary color points according to apredetermined standard by which color difference signals having a firstnumerical range are assigned to an integral value in a first integralrange which is smaller than an integral range which can be expressed bya plurality of bits, into second color signals based on primary colorsaccording to said predetermined standard; converting said second colorsignals into third color signals according to photoelectric transducercharacteristics defined in a numerical range which is greater than anumerical range of color signals corresponding to a luminance signal andcolor difference signals according to said predetermined standard; andconverting said third color signals into a luminance signal and colordifference signals; wherein said luminance signal comprises a luminancesignal according to said predetermined standard and said colordifference signals comprise color difference signals in a secondnumerical range containing said first numerical range, said colordifference signals being assigned to an integral value in the secondnumerical range which can be expressed by said plurality of bits;wherein said signal processing method comprises the steps of:converting, by the processor, said luminance signal according to saidpredetermined standard and said color difference signals in said secondnumerical range into said third color signals; converting, by theprocessor, said third color signals into said second color signalsaccording to said photoelectric transducer characteristics; converting,by the processor, said second color signals into said first colorsignals; and correcting, by the processor, said first color signals intosignals in a numerical range which can be displayed by a displaymechanism for displaying an image.
 10. A program on a computer-readablemedium and executable by a computer for enabling the computer to performa signal processing process for processing a luminance signal and colordifference signals and outputting color signals, wherein said luminancesignal and said color difference signals comprise a luminance signal andcolor difference signals obtained by: converting first color signalshaving primary color points in a wider color range than primary colorpoints according to a predetermined standard by which color differencesignals having a first numerical range are assigned to an integral valuein a first integral range which is smaller than an integral range whichcan be expressed by a plurality of bits, into second color signals basedon primary colors according to said predetermined standard; convertingsaid second color signals into third color signals according tophotoelectric transducer characteristics defined in a numerical rangewhich is greater than a numerical range of color signals correspondingto a luminance signal and color difference signals according to saidpredetermined standard; and converting said third color signals into aluminance signal and color difference signals; wherein said luminancesignal comprises a luminance signal according to said predeterminedstandard and said color difference signals comprise color differencesignals in a second numerical range containing said first numericalrange, said color difference signals being assigned to an integral valuein the second numerical range which can be expressed by said pluralityof bits; wherein said signal processing process comprises the steps of:converting said luminance signal according to said predeterminedstandard and said color difference signals in said second numericalrange into said third color signals; converting said third colorsignals- into said second color signals according to said photoelectrictransducer characteristics; converting said second color signals intosaid first color signals; and correcting said first color signals intosignals in a numerical range which can be displayed by a displaymechanism for displaying an image.